The bending machines which are used at present in order to bend tubes of this type conventionally comprise a frame, on which there are mounted bending means, which are provided with support surfaces, between which the tube to be bent passes, is clamped and then bent, the bending means being mounted on a bending head, which can pivot around an axis which is coaxial relative to the axis of the bending block. In addition, these bending machines generally comprise a guide rule, which is disposed upstream of the clamping jaw, and optionally a fold-remover component, which is disposed upstream of the bending block. Finally, they comprise means for longitudinal displacement of the tube relative to the frame.
The main disadvantage of these bending machines consists in the fact that they permit bending of the tubes only on a single side, either towards the right or towards the left. Furthermore, the positioning assembly of the clamping jaw, and the assembly for displacement of the rule, require a space which limits the geometry of the finished bent parts.
In order to eliminate the disadvantage relative to the single direction of bending, three main types of bending machines exist at present.
Firstly, a first solution consists of providing the bending machines with a numerically controlled gripper, which is designed to rotate the tube around its axis, in order to change the direction of bending. However, bending machines of this type have a first disadvantage, which is derived from the fact that during changes of the direction of bending, the movements of the tube generate so-called "whip" phenomena, which in particular can detract from the shape of the part produced.
A second solution consists of providing bending machines which are provided with means for entrainment in rotation of the bending head, which can make the latter rotate around the tube. However, at present, this solution is used exclusively with tubes which are packed onto bobbins, and not with tubes which are pre-cut, and which are previously provided with connections. It has been found that putting these connections into place is more complex and takes longer when it is carried out on products which are bent initially.
Finally, a third solution consists of providing bending machines which have a double bending head, which is associated with means for entrainment in rotation and/or in translation, which make it possible to bring the second bending head into the working position. However, this solution leads to production of bending machines which are relatively complex and large, and thus have a high cost price. In addition, the change of direction of bending makes it necessary to displace the bending heads, and this operation requires a relatively long period of time, which detracts from the productivity of the machine.